Willie Mays, 1971.
Here is what Baseball Reference says about Power-Speed #
"2 x (Home Runs x Stolen Bases)/(Stolen Bases + Home Runs) The harmonic mean of HR and SB. To do well you need a lot of both. Developed by Bill James."
Mays led the league in with a .425 OBP. The NL average was just .316
His SB% was 88.46% (23-3). The league average was 64.7%.
His Power-Speed # was 20.2. Only 25 year old Bobby Bonds (Barry's dad) was higher with 29.1 (Mays hit 18 HRs).
Mays is the only player at least 37 years old to have at least 15 HRs, 20 SBs, and a .400+ OBP. Only 1 guy did it at age 36 (Molitor).
Mays is the only player 40+ years old to steal 20+ bases with at least an 80% success rate.
He was 5th in the NL in WAR for position players with 6.3. The Giants won their division by a single game over the Dodgers.